Close Encounters

Global warming will limit opportunities for a sexually-deceptive orchid

Leporella fimbriata, the Hare Orchid, relies upon one species for pollination. A new study by Marta Kolanowska and colleagues in Czechia and Poland has looked at the impact of global warming on the orchid. They didn’t just look at the effect of rising temperatures on the plant but also on its partner pollinator too. They found that while the orchid could live in a warmer climate, its pollinator would lose habitat. As a result, the orchid will lose the opportunity to reproduce in many areas where it would otherwise be viable.

A diagram showing the effects of change in the range of Leporella fimbriata and Myrmecia urens on changes in pollinator availability
Graphical abstract. Source: Kolanowska et al. 2021.

Leporella fimbriata, also known as the hare orchid or fringed hare orchid, gets its name from its lateral petals that stick up like the ears of a hare. It has an unusual pollination method, even by the standards of orchids. It’s a sexually deceptive orchid. Sexual deception in itself is not that unusual. All over the world, orchids have discovered they don’t need to provide food to attract pollinators. Instead, they look like a potential mate for a pollinator and release the right scent to attract a partner who isn’t thinking with their brain. The coupling is disappointing for the insect, who flies off to find another mate. Should they find another orchid masquerading as a partner, then at least the orchids are satisfied, even if the insect is frustrated.

What makes the hare orchid is the pollinator it deceives. It hoodwinks Myrmecia urens, a bulldog ant. Ant pollination is comparatively rare, as often ants have glands that can kill pollen. The way the orchid exploits the ant is by mimicking the queen ant when it flowers. Male ants are attracted to the flowers by scent from the petal tips. The ant climbs onto the labellum and attempts mating. If it’s carrying pollinia, these get pressed to the stigma surface. When the ants leave frustrated, they twist and pick up another batch of pollinia. They then fly off searching for a queen, but they deliver pollen to another plant should they be deceived by another orchid.

Leporella fimbriata. Image: Trex21 / Wikimedia.

Kolanowska and colleagues used ecological niche modelling to examine how both L. fimbriata and M. urens could respond to rising temperatures. To do this, they compiled databases on the habitats of the two species. They then used three machine-learning algorithms to produce ecological niche models.

Comparing the results from the models with current known distributions of the orchids and ants, the team found a strong correlation between the models’ predicted niches and the locations where the species were found. However, the authors note that the model based on soil and climate data did not indicate all regions where the orchid and ant had been found.

For the future, the models tend to suggest that more locations will become suitable for L. fimbriata. These results indicate that things will improve for the orchid. The tale for its pollinator is very different. The sexual deception of L. fimbriata means that its success offers nothing to the ant. “For M. urens all three models are consistent in estimating significant loss of habitats of this species… The reduction of the range of the ant will be observed in the north and north-western parts of the currently occupied areas. The additional suitable habitats for the ant will become available in Tasmania and New Zealand,” write Kolanowska and colleagues.

The authors note that the critical factor for the orchid is how its range will overlap with the ants. Models suggest that the current overlap means that the ant serves around 85% of the places where the orchid could live. In a warmer climate, that figure drops to nearer 60%. It’s not that the orchid would suffer in higher temperatures, but that the lack of pollination means there will be no seeds to seize the opportunities of many niches.

As well as overlap, the authors argue that the orchid could face further challenges in securing pollination. They write, “Pollination events within Leporella population tend to be highly episodic, lasting only one to several days. Probably this timetable is related with the lifespan and flight period of male M. urens. However, pollination episodes can occur anytime between late April and late June. Male ants are mostly active between noon and 4 pm and their activity depends on warm (18–26 °C) and fine weather (Pridgeon et al., 2001). In our research modifications of the flowering season of L. fimbriata and mating flights time of M. urens was not examined due to the scarce observations of the studied ant species.”

The change in flowering season could be devastating if it cannot keep up with the flying period of M. urens. If the ants have all flown before the flowers open, then no pollinators will arrive. The authors also note that it’s not simply a matter of synchronisation.

Willmer (2014) suggested also that beyond the simple timing effects, the climate changes can led to daily pattern disruptions and blurred visual and olfactory signals reaching the pollinators. This may disturb the accurate interaction between pollen vectors and the flowers,” write Kolanowska and colleagues.

Another factor they add is the problem of finding a mycorrhizal partner. Orchids need fungi to grow, and these fungi will have their own reactions to a changing climate. However, new research has found that not all mycorrhizal fungi depend on their hosts in Australia.

The results show that simple modelling of the orchid isn’t enough to determine its likely future. To see what lies in store for the orchid, you have to understand its pollinator, and this is a problem, say Kolanowska and colleagues. “[A]lmost nothing is known about ecology of M. urens. This ant was formally described in 1865 but still there are no information about its reproduction, preferred food sources and phenology. These information is crucial to evaluate the possibility of migration of the species into suitable habitats indicated in our study.”